After Prohibition, the federal government issued the Federal Alcohol Administration Act of 1935, which provided guidelines for four distinctive styles of American straight whiskey: bourbon, rye, wheat, and malt. Each uses a different grain (or blend of grains) as the focal point. Now, Woodford Reserve is one of the first whiskey brands to offer all four of those unique expressions based on those standards.
https://fortune.com/2019/07/28/woodford-reserve-wheat-whiskey/